Organic light emitting diode display and method for manufacturing the same

ABSTRACT

An organic light emitting diode display includes a substrate, first electrodes patterned on the substrate, pixel defining layers on the substrate to separate the first electrodes corresponding to pixel units, light emitting layers on the first electrodes and separated corresponding to the pixel units, and a second electrode on the light emitting layers, wherein the pixel defining layers have pores.

CROSS-REFERENCE TO RELATED APPLICATIONS

This divisional application claims priority to and the benefit of U.S.application Ser. No. 13/584,758 filed Aug. 13, 2012, which claimspriority to and the benefit of Korean Patent Application No.10-2012-0022142, filed in the Korean Intellectual Property Office onMar. 5, 2012, the entire contents of all of which are incorporatedherein by reference.

FIELD

Embodiments of the present invention relate to an organic light emittingdiode display and a method for manufacturing the same.

BACKGROUND

An organic light emitting diode (OLED) display is a self-luminousdisplay device that is provided with organic light emitting diodes thatemit light to display an image. Unlike a liquid crystal display, theorganic light emitting diode display does not require a separate lightsource, and thus the thickness and weight thereof can be relativelyreduced. Moreover, the organic light emitting diode display exhibitshigh quality characteristics such as low power consumption, highluminance, a high response speed, and the like, and thus is in thespotlight as a next generation display device of a portable electronicapparatus.

FIG. 1 schematically illustrates a general structure of an OLED/pixelunit of an organic light emitting diode display.

Referring to FIG. 1, a positive electrode 20 as a first electrode isformed on a substrate 10 for the organic light emitting diode display,and the positive electrode 20 is divided into pixel units using pixeldefining layers (PDLs) 30. A light emitting layer 50 is formed on thepositive electrode 20 and a portion of the pixel defining layers 30. Anegative electrode 70 is formed as a common electrode on the lightemitting layer 50 and the pixel defining layers 30.

Before forming the light emitting layer 50, at least one of a holeinjection layer and a hole transporting layer may be additionallyformed, and at least one of an electron transporting layer and anelectron injection layer may be formed between the light emitting layer50 and the negative electrode 70. Multiple light emitting layers 50 maybe separated into a red light emitting layer, a green light emittinglayer, and a blue light emitting layer.

Currently, light extraction efficiency of the light emitting diodedisplay is approximately 20%, which is not satisfactory. In other words,only about 20% of light generated from the light emitting layer of thelight emitting diode display is emitted outside through a light emittingsurface, and about 80% of light generated from the light emitting layeris confined and extinguished in, or absorbed by, the structure of theorganic light emitting diode display.

The extinguished light partially leaks out to the side of the lightemitting layer of the organic light emitting diode display. That is, anarrow in FIG. 1 denotes that a part of light generated from the lightemitting layer of the organic light emitting diode display is emitted tothe side to be incident on the pixel defining layer. As shown in FIG. 1,a part of the light generated from the light emitting layer of theorganic light emitting diode display is emitted to the side and isincident on the pixel defining layer, and thereafter is extinguished,whereby a part of the light cannot contribute to light emission of theorganic light emitting diode display and leaks out.

If the light leaking to the side is allowed to contribute to the lightemission, it is possible to enhance light extraction efficiency of theorganic light emitting diode display.

SUMMARY

Embodiments of the present invention improve luminous efficiency of anorganic light emitting diode display by allowing light, which isotherwise emitted from a light emitting layer of an organic lightemitting diode display to the side thereof, thereafter leaking out andbeing extinguished, to instead be emitted to a light emitting surface ofthe organic light emitting diode display.

Specifically, embodiments of the present invention allow light, which isemitted from the light emitting layer of the organic light emittingdiode display and incident on a pixel defining layer at the side of thelight emitting layer, to be externally emitted without beingextinguished in the pixel defining layer to thereby contribute to lightemission by changing a path of the light.

To this end, embodiments of the present invention provide an organiclight emitting diode display with enhanced luminous efficiency byforming pores in a pixel defining layer such that light incident on thepixel defining layer is scattered and emitted toward a light emittingsurface.

An exemplary embodiment of the present invention provides an organiclight emitting diode display including a substrate, first electrodespatterned on the substrate, pixel defining layers on the substrate toseparate the first electrodes corresponding to pixel units, lightemitting layers on the first electrodes and separated corresponding tothe pixel units, and a second electrode on the light emitting layers,wherein the pixel defining layers have pores.

The pixel defining layer may include a light transmissive insulatingpolymer.

The light transmissive insulating polymer may include polyimide (PI).

A range of diameters of the pores may be about 10 nm to about 200 nm.

A ratio of a volume of the pores to a total volume of the pixel defininglayer may be about 5% to about 50%.

The organic light emitting diode display may further include one or morefirst light emitting auxiliary layers between the light emitting layersand the first electrodes.

The first light emitting auxiliary layer may include at least one of ahole injection layer or a hole transporting layer.

The organic light emitting diode display may further include a secondlight emitting auxiliary layer between the light emitting layers and thesecond electrodes.

The second light emitting auxiliary layer may include at least one of anelectron injection layer or an electron transporting layer.

The first electrode may be a positive electrode, and the secondelectrode may be a negative electrode.

Another exemplary embodiment of the present invention provides a methodfor manufacturing the organic light emitting diode display, the methodincluding preparing a substrate, forming a pattern of first electrodeson the substrate, forming pixel defining layers between the patternedfirst electrodes, forming light emitting layers on the first electrodes,and forming a second electrode on the light emitting layers, wherein theforming of the pixel defining layers includes preparing a material forforming a pixel defining layer, coating the material for forming a pixeldefining layer on the substrate and the first electrodes, patterning thecoated material for forming a pixel defining layer to form pixeldefining layers such that the first electrodes are partially exposed,and forming pores in the pixel defining layers.

The material for forming a pixel defining layer may include a lighttransmissive insulating polymer, a surfactant, and a solvent.

The light transmissive insulating polymer may include polyimide.

The surfactant may include NaDDBS.

The pores may be formed by processing the pixel defining layers with asolvent.

The pixel defining layers may be processed with the solvent by immersingthe substrate with the pixel defining layers in the solvent.

The method may further include curing the pixel defining layers afterthe pores are formed.

The method may further include forming one or more first light emittingauxiliary layers before the light emitting layers are formed.

The first light emitting auxiliary layer may be formed by forming atleast one of a hole injection layer or a hole transporting layer.

The method may further include forming one or more second light emittingauxiliary layers before the second electrode is formed and after thelight emitting layers are formed.

The second light emitting auxiliary layer is formed by forming at leastone of an electron transporting layer or an electron injection layer.

According to an exemplary embodiment of the present invention, in theorganic light emitting diode display, since the pixel defining layer hasthe pores, light, which leaks to the side from the inside of the organiclight emitting diode display, is extracted by a scattering effect,thereby increasing light efficiency.

Further, according to an exemplary embodiment of the present invention,a scattering layer may be formed without using a scattering agent in thepixel defining layer, such that light leaking to the side is extracted,thereby increasing light efficiency.

In addition, the organic light emitting diode display according to anexemplary embodiment of the present invention has a relatively simplestructure and can improve luminance.

The foregoing summary is illustrative only, and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a general structure of an OLED/pixel unit of anorganic light emitting diode display in the related art, and illustratesa state in which light generated from a light emitting layer is emittedto a pixel defining layer and extinguished, the general direction of thelight being indicated by arrows.

FIG. 2 schematically illustrates a structure of an OLED/pixel unit of anorganic light emitting diode display according to an exemplaryembodiment of the present invention, and illustrates a state in whichlight generated from a light emitting layer is emitted to a pixeldefining layer and scattered to be emitted toward a light emittingsurface.

FIGS. 3A to 3I are cross-sectional views for describing a method formanufacturing an organic light emitting diode display according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

The present invention may be modified to be in various forms, and onlyspecific exemplary embodiments are shown in the drawings and will bedescribed representatively below. However, the scope of the presentinvention is not limited to the specific exemplary embodiments, andshould be construed as including all the changes, equivalents, andsubstitutions included in the spirit and scope of the present invention.

Terms used herein are general terms that are widely used now. In somecases, however, terms selected at the applicant's discretion are alsoused, and the meanings thereof should be comprehended in considerationof meanings described or used in the detailed description of theinvention.

In order to elucidate the present invention, parts that do not relate tothe description may be omitted, and like reference numerals designatelike elements throughout the specification. In the drawings, the sizeand the thickness of each element are arbitrarily represented for easeof description and the present invention is not limited to those shownin the drawings.

In the drawings, the thicknesses of layers, regions, etc., may beexaggerated for clarity and/or ease of description. It will beunderstood that when an element such as a layer, film, region, orsubstrate is referred to as being “on” another element, it can bedirectly on the other element, or intervening elements may also bepresent.

FIG. 2 schematically illustrates a structure of an example of anOLED/pixel unit of an organic light emitting diode display according toan exemplary embodiment of the present invention. Herein, particularly,a pixel unit is restrictively and schematically illustrated for betterunderstanding of the described embodiment of the present invention.

As shown in FIG. 2, the OLED/pixel unit of the organic light emittingdiode display according to an exemplary embodiment of the presentinvention basically includes a substrate 100; a first electrode 200patterned and formed on the substrate; pixel defining layers 300 formedon the substrate to divide the first electrode into pixel units; a lightemitting layer 500 formed on the first electrode and dividedcorresponding to the pixel units; and a second electrode 700 formed onthe light emitting layer.

As shown in FIG. 2, pores 310 are formed in the pixel defining layers300 of the organic light emitting diode display according to embodimentsof the present invention. The pores are generally filled with air. Arefractive index of air is generally smaller than a refractive index ofthe pixel defining layer. Therefore, the pores filled with the air serveas light scattering particles to change a path of light that is incidenton the pixel defining layer.

Arrows in FIG. 2 denote a path of light and show that the light, whichis emitted from the light emitting layer and incident on the pixeldefining layer 300, is refracted at the pores 310, such that the path ischanged and the light is scattered toward a light emitting surface, thuscontributing to light emission of the organic light emitting diodedisplay. As described above, according to embodiments of the presentinvention, the pores 310 are formed in the pixel defining layer 300 ofthe organic light emitting diode display, thereby enhancing luminousefficiency of the organic light emitting diode display.

Hereinafter, the present embodiment of the present invention will bedescribed based on the case where polyimide (PI) is used as a materialfor forming a pixel defining layer (e.g., PDL 300). A refractive indexof polyimide (PI) as a material for forming the pixel defining layer 300is 1.6 (n=1.6), and a refractive index of air is 1.0. Thus, a differencebetween the two refractive indices is about 0.6. When this difference isabout 0.6, comparatively excellent light refracting and light scatteringeffects may be exhibited, and the pores 310 serve as refraction points.In this way, when the pores 310 are formed in the pixel defining layer300, an effect equivalent to adding a light scattering agent to thepixel defining layer 300 may be achieved.

It is generally difficult to add the light scattering agent in a form offine particles, while the pores may be formed in a size on the order ofnanometers, and the light scattering agent has electric conductivity inmany cases, while the air has an excellent electrical insulatingproperty, and thus, is suitable for the pixel defining layer requiringan insulation property.

Sizes and density of the pores 310 formed in the pixel defining layer300 may vary according to a size, a thickness, and a kind of the pixeldefining layer 300.

In an exemplary embodiment of the present invention, a ratio of a volumeof the pores 310 to a total volume of the pixel defining layer 300 maybe 5% to 50%. In other words, the volume of the pores may be 5% to 50%of the total volume of the pixel defining layer. The volume ratio of thepores may be such that the ratio of the volume of the pores 310 to thetotal volume of the pixel defining layer 300 is 10% to 20%. The densityof the pores (e.g., the number and size of the pores) may vary accordingto a material, a size, and a thickness of the pixel defining layer.

The sizes of the pores 310 may be represented by an average diameter,and the diameters of the pores 310 may be in a range of 10 to 200 nm.When the average diameter of the pores is less than 10 nm, effects dueto the light refracting and scattering due to the pores may be reduced,and when the average diameter of the pores is more than 200 nm, thestrength of the pixel defining layer may be reduced, which may be anobstacle to performing an intrinsic function of the pixel defininglayer. Therefore, the average diameter of the pores 310 is limited asdescribed above. A deviation in the diameters of individual pores fromthe average diameter may be possible. The average diameter of the poresof the present embodiment may be 100 to 200 nm.

In order to obtain the pores 310 of the pixel defining layer 300, amethod of mixing the material for forming a pixel defining layer and asurfactant with a solvent to form a pixel defining layer, and thendissolving the surfactant by using a solvent that can dissolve thesurfactant is used, thus forming the pores 310. In this case, thediameters and the volume of the pores 310 may be adjusted by aconcentration of the surfactant to be mixed.

As described above, the light emitting layer 500 is formed on the pixeldefining layer 300 with the pores 310, and the second electrode 700 isformed on the light emitting layer 500, thereby configuring the organiclight emitting diode display.

FIGS. 3A to 3I schematically show an exemplary embodiment of a processfor manufacturing an organic light emitting diode display according tothe present invention.

Hereinafter, a method for manufacturing an organic light emitting diodedisplay will be described, and respective constituent elements of theorganic light emitting diode display will be described in more detail.

First, a substrate 100 is prepared and a material 201 for forming afirst electrode is coated on the substrate (FIG. 3A).

The process of preparing the substrate may include preparing thesubstrate, forming a TFT layer, and forming an insulating andplanarizing layer. In the present exemplary embodiment, a description ofthese processes is omitted. The substrate may be selected and used fromthose generally used in the art. For example, a glass substrate or aplastic substrate may be used.

As a method of coating the material 201 for forming a first electrode, amethod which is generally used in the art may be applied. An example ofthe method includes a sputtering method, although methods other than thesputtering method may also be applied.

The first electrode 200 may include at least one of a transparentconductive oxide (TCO) layer and a metal layer. Therefore, the processof coating the material 201 for forming a first electrode so as to formthe first electrode 200 may include at least one of forming atransparent conductive oxide (TCO) layer and forming a metal layer.Herein, the transparent conductive oxide (TCO) layer may include atleast one of an ITO layer, an IZO layer, and an AZO layer. The metallayer may include at least one of a silver (Ag) layer, a copper (Cu)layer, and an aluminum (Al) layer.

Meanwhile, the first electrode 200 may have a structure in which an ITOlayer, a silver (Ag) layer, and an ITO layer are sequentially stacked,such as by forming the ITO layer, forming the silver (Ag) layer, andforming the ITO layer in sequence.

The first electrodes 200 are formed by patterning the material 201 forforming a first electrode that is coated on the substrate 100 (FIG. 3B).As a patterning method, a method which is generally used in the art maybe applied.

A material 301 for forming a pixel defining layer is coated on thepatterned first electrodes 200 and the substrate 100 (FIG. 3C).

The material 301 for forming a pixel defining layer is prepared bymixing a light transmitting insulating polymer as a material of a pixeldefining layer, a surfactant, and a solvent at a predetermined ratio.Other materials required for forming a pixel defining layer may befurther included. In an exemplary embodiment, the surfactant is includedsuch that a weight of the surfactant is 5% to 50% of a total weight ofthe light transmitting insulating polymer and the surfactant (e.g.,[surfactant/(light transmitting insulating polymer+surfactant)]).

In this case, a kind of light transmitting insulating polymer is notparticularly limited. In the present exemplary embodiment, the casewhere polyimide (PI) is used as the light transmitting insulatingpolymer is described as an example. As the surfactant, NaDDBS and thelike, which are dissolved in water or an organic solvent, may be used.In the present exemplary embodiment, polyimide (PI) mixed with NaDDBSand toluene is used.

Pixel defining layers 300 are formed by patterning the coated material301 for forming a pixel defining layer (FIG. 3D). As the patterningmethod, a method which is generally used in the art may be applied.

The pixel defining layers 300 are formed between the first electrodes200 such that top portions of the first electrodes 200 are exposed.

In this regard, FIG. 3D shows a state where the pixel defining layers300 are formed between the first electrodes 200. Herein, the topportions of the first electrodes are partially opened.

Pores 310 are formed in the pixel defining layers 300 (FIG. 3E). Theforming of the pores 310 includes processing the pixel defining layers300 with a solvent. As an example of the method, a method of immersingthe substrate 100 with the pixel defining layers 300 in a solvent may beused. In this case, the solvent is not limited if the solvent candissolve the surfactant used in the material 301 forming a pixeldefining layer, and water may be used.

As described above, the surfactant is dissolved by water in the pixeldefining layers 300, such that the pores 310 are formed at locationswhere the surfactant was present in the pixel defining layers 300.Therefore, the volume and the diameters of the pores 310 may be adjustedby a concentration of the surfactant that is mixed in the material 301for forming a pixel defining layer.

In the present exemplary embodiment, the volume of the pores 310 may be5% to 50% of the total volume of the pixel defining layers 300. In thepresent exemplary embodiment, the volume of the pores is in a range of10% to 20%. The diameters of the pores 310 may be 10 to 200 nm. In thepresent exemplary embodiment, the average diameter of the pores 310 is100 to 200 nm. The density (volume ratio) and the average diameter ofthe pores may be adjusted by adjusting the content of the surfactant.

Herein, when the average diameter of the pores is less than 10 nm, it isdifficult to expect a scattering effect due to the pores. When theaverage diameter is more than 200 nm, the integrity of the pixeldefining layer may be weakened, which may make it difficult to performan intrinsic function of the pixel defining layer.

Next, the method for manufacturing an organic light emitting displaydevice may include curing the pixel defining layers 300 to performsubsequent steps, such as forming light emitting layers on the pixeldefining layers 300 with the pores 310. A curing method may include heattreatment and the like.

Referring to FIG. 3F, in the process according the present exemplaryembodiment, a first light emitting auxiliary layer 400 is formed beforeforming light emitting layers. The first light emitting auxiliary layer400 is formed over the entire surface of the top portions of the firstelectrode 200 and the pixel defining layers 300. The first lightemitting auxiliary layer 400 may include any one of a hole injectionlayer and a hole transporting layer or both the hole injection layer andthe hole transporting layer.

FIG. 3F illustrates that a hole injection and transporting layer havingboth a hole injection function and a hole transporting function isformed in one layer. For reference, the forming of the first lightemitting auxiliary layer 400 may include any one of forming a holeinjection layer and forming a hole transporting layer, or may includeboth steps.

For example, the first light emitting auxiliary layer 400 may includetwo layers such that a hole injection layer may be formed, andthereafter, a hole transporting layer may be formed.

Subsequently, light emitting layers 510, 520, and 530 are formed on thefirst light emitting auxiliary layer 400 (FIG. 3G). The light emittinglayers 510, 520, and 530 are positioned above the first electrodes 200comprising the pixel units that are separated by the pixel defininglayers 300.

Referring to FIGS. 3H and 3I, in the process according to the presentexemplary embodiment, after forming the light emitting layers, a secondlight emitting auxiliary layer 600 is formed before forming a secondelectrode 700.

The second light emitting auxiliary layer 600 may include at least oneof an electron injection layer and an electron transporting layer.Therefore, the forming of the second light emitting auxiliary layer mayinclude at least one of forming an electron transporting layer; andforming an electron injection layer.

In the present exemplary embodiment, for example, the second lightemitting auxiliary layer 600 is an electron transporting layer.Therefore, in FIG. 3H, an electron transporting layer is formed as thesecond light emitting auxiliary layer 600. The second light emittingauxiliary layer 600 may include two layers so as to separately includeboth the electron injection layer and the electron transporting layer.

Thereafter, a second electrode 700 is formed on the second lightemitting auxiliary layer 600 (FIG. 3I).

The organic light emitting diode display according to the presentinvention may be manufactured through the aforementioned processes.

Another exemplary embodiment of the present invention provides a methodfor manufacturing an organic light emitting diode display, the methodincluding preparing a substrate, forming a pattern of first electrodeson the substrate, preparing a material for forming a pixel defininglayer; coating the material for forming a pixel defining layer on thesubstrate and the first electrodes, patterning the coated material forforming a pixel defining layer to form pixel defining layers such thatthe first electrodes are partially exposed, processing the pixeldefining layers with water to form pores, curing the pixel defininglayers after forming the pores, forming light emitting layers on thefirst electrodes, and forming a second electrode on the light emittinglayers.

The organic light emitting diode display according to exemplaryembodiments of the present invention can maintain the intrinsic functionof the pixel defining layer without using a separate scattering agent.Therefore, the organic light emitting diode display may have a simpleconfiguration compared to an organic light emitting diode display in therelated art which introduces a scattering agent or a polarizing plate ina pixel defining layer, and can ensure improved light efficiency andluminance by a scattering effect.

From the foregoing, it will be appreciated that various embodiments ofthe present invention have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present invention.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims, and their equivalents.

What is claimed is:
 1. A method for manufacturing an organic lightemitting diode display, the method comprising: preparing a substrate;forming a pattern of first electrodes on the substrate; forming pixeldefining layers between the patterned first electrodes; forming lightemitting layers on the first electrodes; and forming a second electrodeon the light emitting layers, wherein the forming of the pixel defininglayers comprises: preparing a material for forming the pixel defininglayers; coating the material for forming the pixel defining layers onthe substrate and the first electrodes; patterning the coated materialfor forming the pixel defining layers to form pixel defining layers suchthat the first electrodes are partially exposed; and forming pores inthe pixel defining layers.
 2. The method of claim 1, wherein thematerial for forming the pixel defining layers comprises a lighttransmissive insulating polymer, a surfactant, and a solvent.
 3. Themethod of claim 2, wherein the light transmissive insulating polymercomprises polyimide.
 4. The method of claim 2, wherein the surfactantcomprises NaDDBS.
 5. The method of claim 1, wherein the pores are formedby processing the pixel defining layers with a solvent.
 6. The method ofclaim 5, wherein the pixel defining layers are processed with thesolvent by immersing the substrate with the pixel defining layers in thesolvent.
 7. The method of claim 1, further comprising: curing the pixeldefining layers after the pores are formed.
 8. The method of claim 1,further comprising: forming one or more first light emitting auxiliarylayers before the light emitting layers are formed.
 9. The method ofclaim 8, wherein the first light emitting auxiliary layer is formed byforming at least one of a hole injection layer or a hole transportinglayer.
 10. The method of claim 1, further comprising: forming one ormore second light emitting auxiliary layers before the second electrodeis formed and after the light emitting layers are formed.
 11. The methodof claim 10, wherein the second light emitting auxiliary layer is formedby forming at least one of an electron transporting layer or an electroninjection layer.